1. Field of the Invention
The present invention relates, in general, to the regulation of pressurized air in self-contained underwater apparatus, and it relates more particularly to improving the operation of a second stage demand type regulator which exhibits free flowing characteristics due to the effects of venturi action.
2. Description of the Prior Art
Breathing apparatus of the type used in underwater diving systems commonly employs a two stage regulator arrangement for controlling the flow of air from a pressurized air supply tank. A first stage regulator is generally mounted directly to the air supply tank and is connected it to a second stage regulator by a single length of flexible hose. The second stage regulator usually includes a lightweight housing adapted with a mouthpiece which is capable of being comfortably retained within the mouth of the user. Within the housing is a flexible diaphragm which provides a breathing chamber through which the user inhales and exhales air. The diaphragm is connected to an air inlet valve and, on the side opposite the breathing chamber, it is exposed to ambient pressure such that as the user inhales, the diaphragm collapses toward the breathing chamber, opening the air inlet valve and admitting pressurized air into the breathing chamber. Exhalation of air by the user causes increased pressure within the breathing chamber thereby deflecting the diaphragm outwardly of the breathing chamber and causing the valve to close. A check valve arrangement provided in a wall of the breathing chamber permits air to be exhausted from the regulator as the user continues to exhale.
Regulators of the foregoing type can be designed to perform reliably with relatively few operative components. However, their simplicity belies the difficulties that have been encountered in providing a regulator which operates with minimum breathing effort on the part of the user. One of the characteristics of such regulators is that they tend to free-flow after inhalation by the user has been initiated, causing an air flow condition which does not corespond to the normal breathing requirements of the user. Free-flowing is a condition caused by the venturi effect of the stream of air exiting through the mouthpiece from the breathing chamber resulting in sustained relatively low pressure in the breathing chamber after the user ceases to inhale. The sustained low pressure within the breathing chamber causes the diaphragm to remain collapsed such that the valve continues to admit air into the breathing chamber. While a slight venturi effect is desirable because it enhances the inhalation charateristics of the regulator, extended breathing with a regulator having a tendency to free-flow can be annoying to the user. Moreover, regulator free-flow can be particularly troublesome to the novice or inexperienced diver.
Accordingly, it would be desirable to balance the venturi effect characteristics of a regulator such that venturi action assists the inhalation of air by the user, and yet is easily terminated when the user ceases inhalation. A prior art regulator which recognizes the difficulties associated with balancing venturi effect is disclosed in U.S. Pat. No. 4,182,323 granted Jan. 8, 1980, and assigned to the assignee of the present invention. While such a regulator performs satisfactorily, the need still exists for further refinement of the venturi effect characteristics of regulators, generally.